This invention relates to multiple output DC to DC converters. It finds particular application in conjunction with a voltage controlled preload for the main output of the converter to maintain regulation on the other outputs of the converter and will be described with particular reference thereto. It is to be appreciated, however, the invention has broader applications and maybe advantageously employed in other environments and applications.
DC to DC converters provide a regulated DC output voltage from an unregulated DC input voltage. Many such converters provide both main output and auxiliary output voltages. The operation of the converter switching means is controlled to maintain a regulated voltage at the main output of the converter. The auxiliary output voltages are regulated by the turns ratio of the transformer which couples the auxiliary output circuits to the power switching means. If needed the auxiliary output voltages are further regulated by a post regulator. The load at the main output and the loads on the auxiliary outputs are independent from each other.
The load connected to the main converter output may vary from very light i.e. no load, to very heavy i.e. full load. The loads on the auxiliary outputs also vary from no load to full load. The converter input voltage may also vary over a wide range e.g. three to one. The converter must provide regulated main and auxiliary output voltages for all load conditions, i.e. over the entire load range and over the entire range of input voltage variation. When the converter operates at the no load condition for the main output this requirement of maintaining regulated voltage at the auxiliary output over the entire auxiliary output load range necessitates the use of a preload for the main output. Such a preload can be provided by a resistor. The resistor will, however, degrade the efficiency of the converter by a noneligible amount when the converter operates at full load and does not provide for a linear adjustment of the preload over the entire range of operation. Therefore it is desirable that a preload be adjustable based on the voltage regulation of the auxiliary output. Such a preload will maximize converter efficiency.